Display screen or portion thereof with a graphical user interface of a mobile device



The sole FIGURE is a front view of a display screen with a graphical user interface of a mobile device.

The broken line illustrates the display screen or portion thereof and forms no part of the claimed design. The broken lines illustrate portions of the graphical user interface and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface of a mobile device, as shown and described. 